Interpretive Summary: U.S. federal and state governments are encouraging the production of crops that can be used for biofuels; however, research into the the hydrological impacts of their cultivation is in its infancy. To investigate such issues, scientists from the University of Oklahoma and ARS (Bushland, Texas) studied the response of a 600 square miles semiarid basin in western Oklahoma to increasing production of switchgrass as a biofuel. According to the restuls from a hydrological model, increases in the cultivation of switchgrass resulted in decreases in spring and summer streamflows. These results indicate that the production of switchgrass as a biofuel may not be possible in semiarid areas where river compacts or other regulations require minimum streamflows.

Technical Abstract:
The conversion of land for biofuel cultivation is expected to increase given concerns about the sustainability of current fossil-fuel supplies. Nonetheless, research into the environmental impacts of biofuel crops, primarily the hydrological impacts of their cultivation, is in its infancy. To investigate such issues, response of a 1649 square kilometers semiarid basin to the incremental substitution of the widely-discussed biofuel candidate switchgrass for native land uses was modelled using the Soil and Water Assessment Tool (SWAT). Median discharges decreased 5.6%-20.6% during the spring and 6.4-31.2% during the summer depending on the quantity of acreage converted. These were associated with the increased spring and summer evaporation of 4.3%-46% and 2.2%-24%, respectively, depending on the quantity of switchgrass biomass produced. The substitution of switchgrass also resulted in larger quantities of water stress days. The authors encourage the exploration of alternative biofuel crops in semiarid areas to mitigate such negative impacts.